1. Field
Aspects of the present disclosure relate to wireless communication systems and to timing advance grouping for UL carrier aggregation.
2. Background
Wireless communication networks are widely deployed to provide various communication services such as voice, video, packet data, messaging, broadcast, etc. These wireless networks may be multiple-access networks capable of supporting multiple users by sharing the available network resources. Examples of such multiple-access networks include Code Division Multiple Access (CDMA) networks, Time Division Multiple Access (TDMA) networks, Frequency Division Multiple Access (FDMA) networks, Orthogonal FDMA (OFDMA) networks, and Single-Carrier FDMA (SC-FDMA) networks. As used herein, a “carrier” refers to a radio band centered on a defined frequency and used for wireless communications.
A wireless communication network may include a number of base stations that can support communication for a number of user equipments (UEs). A UE may communicate with a base station via the downlink and uplink. The downlink (or forward link) refers to the communication link from the base station to the UE, and the uplink (or reverse link) refers to the communication link from the UE to the base station.
The 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) represents a major advance in cellular technology as an evolution of Global System for Mobile communications (GSM) and Universal Mobile Telecommunications System (UMTS). The LTE physical layer (PHY) provides a highly efficient way to convey both data and control information between base stations, such as an evolved Node Bs (eNBs), and mobile entities, such as UEs.
To establish initial connection with an eNB, a UE may measure the downlink (or forward link) signals to determine the downlink synchronization. The UE may then send out a random access channel (RACH) preamble in the uplink (or reverse link) direction. Once the eNB receives the RACH preamble, the eNB may estimate a timing difference and send the UE timing advance (TA) information in a random access response (RAR) message. The timing advance may compensate for the propagation delay between the eNB and the UE. The timing advance may vary based on time, due to mobility of the UE. In a TA maintenance phase, the eNB may measure the timing of the received UL data and just the UL timing using the TA command.
LTE UEs may use bandwidth allocated in a carrier aggregation (up to 5 component carriers) for transmission in each direction. Generally, less traffic is transmitted on the uplink than the downlink, so the uplink spectrum allocation may be smaller than the downlink allocation. Component carriers may share a same timing advance value and belong to the same timing advance group (TAG). Another set of component carriers may have a different TAG.